Restructuring of Gold-Palladium Alloyed Nanoparticles: A Step towards More Active Catalysts for Oxidation of Alcohols

Article abstract of DOI:10.1002/cctc.201900553

AuPd alloyed nanoparticles are regarded as very active catalysts for oxidation of alcohols. However we found that their catalytic activity can be further improved after calcination in air, which lead to the restructuring of alloyed AuPd nanoparticles and

Full text of DOI:10.1002/cctc.201900553

Accepted Article
Title: Restructuring of gold-palladium alloyed nanoparticles: a step
towards more active catalysts for oxidation of alcohols
Authors: Tiago A G Silva, Camila P Ferraz, Renato V. Gonçalves,
Erico Teixeira-Neto, Robert Wojcieszak, and Liane Marcia
Rossi
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10.1002/cctc.201900553
ChemCatChem
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Restructuring of gold-palladium alloyed nanoparticles: a step
towards more active catalysts for oxidation of alcohols
Tiago A. G. Silva, [a] Camila P. Ferraz, [a] Renato V. Gonçalves, [b] Erico Teixeira-Neto, [c] Robert
Wojcieszak, [d] Liane M. Rossi*[a]
Abstract: AuPd alloyed nanoparticles are regarded as very active
catalysts for oxidation of alcohols. However we found that their
catalytic activity can be further improved after calcination in air,
which lead to the restructuring of alloyed AuPd nanoparticles and
PdO segregation on the surface. The alloyed character was partially
recovered upon reduction with H2 atmosphere, but the yet Pd-rich
surface was less active in the oxidation of the model molecule
benzyl alcohol.
vinyl acetate production,27 carbon monoxide oxidation,28,29 and
toluene oxidation.30 Prati and Rossi31 and Corma and Garcia32
showed that supported Au NPs are very selective catalysts for
oxidation of alcohols, and good conversion was achieved in the
presence of base or due to the support. Hutchings et al.21
showed that the addition of palladium to form Au–Pd alloy NPs
leads to an enhancement in activity by a factor of ca. 27
compared with the monometallic gold and palladium NP
catalysts, while the aldehyde is also formed with very high
selectivities. Composition effect was also reported, where a
progressive increase in catalytic activity was observed on
increasing the Pd content, with the optimum ratio of Au:Pd in ca.
1:1.85, and a progressive decrease of activity with further
increase in the Pd content.33 The AuPd NPs were dried at 120
oC for 16 h and the experimental surface Pd/Au molar ratios
were obtained by X ray photoelectron spectroscopy (XPS). A
more detailed study of the effect of thermal treatment (120, 200,
300 and 400 oC) on the surface composition and catalytic activity
was also reported for the sample of 1:1.85 Au:Pd molar ratio.34
From the XPS data, Au was reduced, whereas the oxidation
state of Pd progressively changes from Pd0 to Pd2+ with the
increase of calcination temperature. The authors concluded that
there should be an optimum ratio between Pd0–Pd2+ species that
will maintain a high activity as well as high selectivity to
hydrogen peroxide. The catalytic activity of AuPd NPs in the
oxidation of CO is also affected significantly by the different pre-
treatment conditions. Oxidation induces dealloying and
enrichment of PdO on the surface but has a negative effect on
activity, while H2 reduction results in realloying with just slight
Introduction
Bimetallic nanoparticles have received increasing attention in
catalysis due to synergistic effects and the possibility of tuning
the activity by changing the metal-to-metal relative
composition.1,2 However, the structural complexity of bimetallic
catalysts is high, they can restructure during pre-treatment steps
and under reaction conditions, assuming different metal domains
distributions and chemical state.3-9
In the colloidal synthetic route, also known as the sol-
immobilization method, the nanoparticle synthesis and the
deposition on the support are separated into two subsequent
steps allowing the well-controlled properties of bimetallic
nanoparticles (uniform size, controllable morphology and tunable
composition) to be transferred to the supported catalyst. This
control is difficult to achieve following the impregnation-reduction
or deposition synthetic approaches.10,11 The colloidal synthetic
route has been used for the preparation of gold bimetallic
catalysts for some time,12-20 but
a
more complete
surface enrichment of Pd and
a
much higher activity.35
characterization of the bimetallic nanoparticle surface, metal
domain distribution, their chemical state and all possible
restructuring processes after thermal treatments has been
overlooked.
Gold-Palladium nanoparticle (NP) catalysts exhibit remarkable
activity in both aqueous-phase and solventless oxidation of
alcohols and olefins,21-25 direct synthesis of hydrogen peroxide,26
Understanding of structure and composition of AuPd NP
catalysts after pre-treatment under reaction conditions is the key
principle for design a more active catalyst and to find robust
structure-activity relationships. XPS coupled with
X
ray
absorption spectroscopy (XAS) analysis are strong tools for
investigating the surface and bulk compositions of the studied
nanoparticles. The extent of alloying, J,36 which consists of a
comparison of the EXAFS-determined coordination numbers
and the expected coordination numbers in an ideal alloy is
[a]
Prof. Dr.L. M. Rossi, T. A. G. Silva, C. P. Ferraz,
Departamento de Química Fundamental, Instituto de Química,
Universidade de São Paulo, Av. Prof. Lineu Prestes 748, São Paulo,
05508-000, SP (Brazil).
lrossi@iq.usp.br
Prof. Dr. R. V. Goncalves
Instituto de Física de São Carlos, Universidade de São Paulo, CP
369, 13560-970 São Carlos, São Paulo Brazil
Dr. E. Teixeira-Neto
Laboratório de Microscopia Eletrônica, LNNano-CNPEM, C.P. 6192,
13083-970, Campinas, SP, Brazil.
powerful for characterising the structure of
nanostructure.
a bimetallic
Here we investigated the structural properties of freshly-
prepared (untreated) and thermally treated silica-supported
AuPd NPs under air and then reduced in hydrogen atmosphere
(Scheme 1); as a probe to surface activity of bimetallic AuPd
NPs were tested in the oxidation of benzyl alcohol.
[b]
[c]
[d]
Dr. R. Wojcieszak
Univ. Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181 -
UCCS - Unité de Catalyse et Chimie du Solide, F-59000 Lille,
France
Supporting information for this article is given via a link at the end of
the document.
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10.1002/cctc.201900553
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reduced with H2, the Pd/Au ratio decreased to 6.3 (Table 1).
Indeed, the Au content on the surface increased, suggesting Au
migration to the surface and some level of reconstruction of the
alloy-like structure. The binding energies of Au0 4f (4f7/2 = 83.33
eV) and Pd0 3d (3d5/2 = 334.92 eV) are slightly different from the
values observed for Au0 (4f7/2 = 82.98 eV) and Pd0 (3d5/2
334.87 eV) in the untreated sample (Table S1).
=
Scheme 1. Schematic cross-sectional representation of freshly-prepared
alloyed AuPd4 NPs, and proposed structures after calcination in air and after
reduction with molecular hydrogen.
Results and Discussion
AuPd NPs with composition of Au:Pd 1:4 were prepared by the
colloidal synthesis route and supported on silica-coated
magnetite nanoparticles, a support that facilitates the catalyst
separation and recovery. The metal loading measured by F-AAS
was close to 1 wt% (0.23 wt% Au, 0.50 wt% Pd, and atomic ratio
Au:Pd 1:4). The freshly-prepared catalyst was dried at 100oC
and other samples were obtained after calcining the catalyst at
500oC for 2 h in air. The samples were analyzed by TEM and
STEM in order to determine the AuPd NP average particle size.
The mean size of the untreated bimetallic nanoparticles (4.6 ±
2.1 nm) increased only 1 nm after calcination (5.5 ± 1.5 nm)
(Figure 1). However, size-composition diagrams, obtained by
EDS analysis of individual nanoparticles, revealed a broadening
of the nanoparticle composition after calcination, suggesting
metal segregation upon heating (Figure 2). The nominal molar
composition for Au in AuPd alloyed NP is 20% Au, but the
composition of individual particles measured by EDS ranged
from 10 to 25% Au, in the untreated sample, and 0 to 55% Au, in
the calcined sample. The changes in the sample after
calcination were better investigated by XPS, XRD and XAS
(Note: In order to better characterize the prepared catalysts by
solid-state techniques, we prepared mimetic catalysts,
comprised by a non-magnetic silica support, with a metal loading
of 6% (Au + Pd)).
Figure 1. TEM analysis of the untreated and STEM analysis of the calcined
catalyst samples and size distribution histograms.
The surface-composition determined by XPS shown in Figure 3
revealed an increase in surface-Pd after calcination under air,
which suggests the restructuring of the AuPd alloy and Pd
segregation to the surface (Table 1, see SI Table S1 and S2).
The trend in the relative percentages of Pd and Au revealed
important differences in the interaction between these two
metals after thermal treatment. The untreated catalyst has the
chemical composition close to the nominal (Pd:Au atomic ratio of
4). After calcination, the Au surface content decreased
significantly (from 0.8% to 0.39%) and the Pd/Au ratio increased
from 3.5 to 7.9. Along with the increase in surface Pd after
calcination, the oxidation of Pd to Pd2+ species is a strong
evidence of AuPd nanoparticles dealloying and of Pd migration
to the surface. A small amount of Au3+ species (0.12%) was
detected (the Au4f doublet had a 3.67 eV separation between
the Au4f7/2 and Au4f5/2 peaks, and a new doublet presenting a
3.20 eV shift from the Au0 doublet was observed (Figure S1 and
Table S1)). Since most of the Pd segregated on the surface is
oxidized, and only a few gold atoms are located on the surface
after calcination, we may not exclude the presence of single Au
atoms trapped in the PdO lattice. When the calcined sample was
Figure 2. Size-composition diagrams obtained by EDS analysis of the catalyst
samples. Number of individual particles analysed: 50 untreated and 50
calcined samples.
These differences of energy peak locations are due to the
electronic interactions between the Pd and Au after thermal
treatment. Moreover, the freshly-prepared and calcined samples
have comparable metal content (Au+Pd) of about 3.5%.
Contrary, the reduced sample has only 1.2% of the metals on
the surface. This is probably due to a significant increase in
particle size after reduction (Figure 4).
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Figure 5. XRD pattern of the AuPd 1:4 catalysts: untreated, calcined and
reduced after calcination. PdO phase is indicated by star markers.
The XRD patterns obtained for the freshly-prepared, calcined
and reduced (after calcination) catalyst samples are fully
consistent with the XPS results (Figure 5). The XRD pattern of
the untreated sample corresponds to the diffraction peaks of an
alloyed AuPd crystalline phase. The diffraction peak for the
(111) plane is in the middle way between Au (111) and Pd (111)
peaks, which correspond to diffraction peak of AuPd metal alloy
according to Vegard's law. The peak position at 2θ = 39.30 is
Figure 3. XPS Pd 3d region for untreated, calcined and reduced (after
calcination) catalyst samples.
Table 1. XPS analysis of the AuPd 1:4 catalysts. Au and Pd atomic % and
Pd/Au, Pd/Si and Au/Si atomic ratios.
however shifted from the expected value of 2θ = 39.76 for
37,38
Au1Pd4, suggesting a bulk composition of Au1Pd1.3
.
After
Catalyst
Au + Pd (%)
Pd/Au
Pd/Si
Au/Si
sample calcination, the emergence of a new PdO crystal phase
is clear, while the diffraction peak for the (111) plane is now
shifted towards the Au (111) peak, with a bulk composition of
Au4Pd1. From XRD, it is evident that segregation and oxidation
of Pd occurred after calcination. Interestingly, when the calcined
sample was reduced with H2, the diffraction peak for the (111)
plane split into two components, the first component is slightly
shifted to higher 2θ values suggesting the alloy is partially
restored, to a bulk composition of Au1.7Pd1. The second peak is
difficult to assign as it can be either Pd(111) or partially restored
AuPd(111) alloy and Vegard law suggests a bulk composition of
Au1Pd7.3. The presence of a rich palladium phase suggests that
segregation of palladium to the surface is not reversible, and Au
did not completely redissolve in the Pd phase (see SI Figure S2
and Table S3). The diffraction peaks of (220) and (311) planes
are shifted with respect to pure Au crystal phase, which may
give evidence of at least a partial reconstruction of the AuPd
alloy phase.
Pd0
2.47
0.35
0.85
Pd2+
0.31
2.77
0.17
Au0
0.68
0.35
0.16
Au3+
0.12
0.04
-
Untreated
Calcined
Reduced
3.5
7.9
6.3
0.10
0.10
0.03
0.03
0.01
0.004
The samples were analysed by XAS (see S.I. for a detailed
analysis of the XAFS data). Figure 6 displays the Au L3-edge
and Pd K-edge Fourier transformed (FT) EXAFS k3 χ(k) curves
of the freshly-prepared, calcined and reduced (after calcination)
AuPd catalyst samples. The Au L3-edge FT curves show peaks
in the 2-3 Å region formed by the contribution of Au-Au and Au-
Figure 4. TEM analysis of the H2-treated catalyst after calcination (reduced).
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Pd scattering paths that are slightly out of phase. The peak
shape and position were changed with the thermal treatment
conditions. These changes are related to evolution of the
composition of the alloyed phases, creating two peaks in the real
part of the Fourier-transformed EXAFS curve. Furthermore, the
Pd K-edge also shows a peak in the 2-3 Å region, but the
calcined sample reveals an additional peak between 1.2-1.8 Å
from the scattering path Pd-O.
Table 2. Calculated EXAFS coordination numbers and atomic distances. Extent of alloying J determined by the EXAFS-obtained coordination numbers and
corrected by the F-AAS-determined compositions.
Au L3-Edge
Au-Au
Pd K-Edge
Pd-Pd
7±1
J
Sample
R (Å)
Au-Pd
7.2±0.5
2.0±0.3
5.5±0.4
R (Å)
R (Å)
2.780±0.01
-
Pd-Au
3.1±0.9
-
R (Å)
2.77±0.03
-
Pd-PdO
-
3.7±0.3a
0.6±0.3 b
Au
Pd
96
0
Untreated
Calcined
Reduced
2.7±0.3
7.9±0.6
5.0±0.4
2.800±0.01
2.842±0.005
2.820±0.006
2.785±0.005
2.830±0.01
2.798±0.005
107
28
-
9.8±0.8
2.739±0.004
1.3±0.5
2.75±0.04
72
48
aR = 3.036±0.002 Å. bR = 3.02±0.04 Å.
Figure 7. Benzyl alcohol conversion kinetics for the freshly-prepared catalyst
(untreated, open squares), calcined catalyst (open triangles) and H2-treated
catalyst after calcination (reduced, open circle). Dashed lines indicate
selectivity (%) to benzaldehyde. Other minor products formed are benzyl
benzoate and benzoic acid. The calcined sample also formed 0.9% of toluene.
Reaction conditions: 0.75 mg Au + Pd, 9.6 mmol benzyl alcohol, 373.15 K, 6
bar O2.
Figure 6. Au L3 edge and Pd-K edge EXAFS measurements shown in R-
space (k3) for the untreated, calcined and reduced catalyst samples.
The absence of this peak after sample reduction discloses that
the metallic character of the sample can be recovered, but the
increase in intensity of the peak in the 2-3 Å region discloses
additional Au-Pd segregation after reduction. These
observations can be further explained by EXAFS fitting. Table 2
shows the evolution of the EXAFS-calculated coordination
numbers on the Au L3 edge and Pd K-edge, characterizing the
formation of a random alloy for the untreated sample, close to
the ideal structure with prevailing heteroatomic interactions, as
evidenced by calculating the extent of alloying J (Table 2).12 The
value of J calculated for Au is slightly superior to 100 for the
untreated sample, suggesting a greater affinity for heteroatom
bonding. The values of J are, however, very close to 100 for
both Au and Pd, and suggest the formation of a random alloy.
After calcination, metal segregation occurred in the form of Au
and PdO, as observed by XRD. Although Au-Pd interaction
could be determined in the Au L3-edge EXAFS, only PdO was
observed from the Pd K-edge EXAFS, without interactions with
Au atoms. The calcined sample was then reduced with H2 and
most of the PdO was reduced to metallic Pd (Figure 6) and the
alloy was partially restored (J of 48% for Au L3-edge and 72%
for Pd k-edge). These values of J, lower than 100%, suggest
that even though bimetallic character is recovered, homoatomic
interactions are dominant and the sample consists of an Au-rich
alloy and another Pd-phase. These observations can be further
supported by the comparison of the FT EXAFS curves, shown in
R-space (k3), once the Au L3-edge curve is dissimilar to the Au
reference foil and the Pd K-edge curve shows a similar form to
that of the Pd foil.
Since AuPd alloyed nanoparticles receive so much attention as
catalysts for the selective oxidation of alcohols,12-25 we decided
to study any possible effect of surface changes that occurred
upon thermal treatment in oxidizing and reducing atmospheres
on the reaction rates of benzyl alcohol oxidation (Figure 7). The
AuPd nanoparticles after calcination, i.e. the catalysts with PdO
phase, were found to be more active than the freshly-prepared
AuPd alloyed NPs for liquid-phase benzyl alcohol oxidation,
while the high selectivity for benzaldehyde was preserved.
Besides the positive effect expected of cleaning the surfaces
from the capping agents, the segregation of palladium and its
oxidation seems to play a major role in the catalytic activity.
Contrarily, the H2-treated sample; i.e. PdO was converted to
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metallic Pd, showed a drastic drop in activity. Lee et al.39 found a
direct correlation between the presence of PdOx surface sites
and the reactivity in selective oxidation of alcohols over
monometallic Pd catalysts. They also showed that reduction of
PdOx to Pd metal suppresses activity, and that catalyst pre-
reduction likewise dramatically impairs oxidation.40 The
performance of AuPd NP catalysts has mostly been attributed to
nanoalloys that can be formed at any Au and Pd ratios, but the
contribution of PdO to improve the activity of bimetallic AuPd NP
catalysts has been neglected.
equipped with a FEG electron source operating at an acceleration
voltage of 200 kV (LNNano – CNPEM, Campinas, Brazil). Chemical
surface composition was carried out by XPS analysis using a K-Alpha
spectrometer (Thermo Scientific) at the LNNano (CNPEM, Campinas,
Brazil). During the measuring, surface charging was eliminated with a
double beam charge compensator. The pass energy of the analyser was
held at 50 eV for both the survey and high resolution analysis. In these
conditions, the FWHM for the Au4f7/2 peak was 1.5 eV. The shift of
energy spectra was corrected in energy with the Si2p peak (103.5 eV).
The surface atomic concentrations were calculated by correcting the
intensities with theoretical sensitivity factors based on Scofield cross
sections41 and the mean free path varying according to 0.7 power of the
photoelectron kinetic energy. Peak decomposition was performed using
curves with a 70% Gaussian type and a 30% Lorentzian type with an
asymmetric Voigt parameter for Pd and Au, and a Shirley nonlinear
sigmoid-type baseline. The following peaks were used for the quantitative
analysis: O 1s, C 1s, Si 2p, Au 4f and Pd 3d. Moreover, the C 1s peak
was use to check for charge stability as a function of time. The C-(C,H)
component of the C 1s peak of adventitious carbon was fixed to 284.8 eV
to set the binding energy scale, and the data treatment was performed
using CasaXPS software (Casa Software Ltd., U.K.). X-ray powder
diffraction (XRD) measurements were performed using a Ultima IV-
Rigaku diffractometer using Cu-Kα radiation operating at 40kV and 30mA
in the 2-theta range of 20 - 90° with a step size of 0.02° and a dwell time
of 5s per step. XAFS measurements were conducted in the XAFS1 and
XDS beamlines of the Brazilian Synchrotron (LNLS – CNPEM, Campinas,
Brazil, proposals 16100 and 17170). Pd K edge was measured in the
XDS beamline while Au L3 edge was measured in both XAFS1 and XDS
Conclusions
Bimetallic AuPd NPs were first prepared and then immobilized
on the support in order to preserve the properties obtained in the
colloidal synthesis (size and composition). However, the
combination of techniques has allowed us to follow the
restructuring of these bimetallic NPs after thermal treatment in
air and then after reduction with H2 (Scheme 1). The as-
prepared alloyed nanoparticles have restructured into AuPd/PdO
after segregation of palladium and oxidation at the surface. The
Au rich core-PdO rich shell became much more active for the
oxidation of benzyl alcohol than the homogeneous alloy. We
believe the remarkable effect of restructuring and dealloying
should not be neglected due to a significant change in the
catalytic activity. Metal segregation under reaction conditions
has also to be taken into account in the study of other gold
bimetallic catalysts. The effect of thermal treatments in AuPd
alloys of different compositions is under study in our group.
beamlines. Measurements were conducted using
a
Si(111)
monochromator for the Au L3 edge and a Si(311) monochromator for the
Pd K edge. Spectra analysis was conducted with the IFEFFIT library
using the GUI Athena and Artemis.42 All spectra were energy calibrated
to the first inflection point of the Au L3-edge and Pd K-edge at 11919 eV
and 24350 eV respectively and normalized in Athena, using a linear pre-
edge and a third order polynomial post-edge for background subtraction.
EXAFS signal was extracted in Athena with a R = 1.0 cut-off and k weight
= 2 and Fourier transformed using a Hanning window in k3 and dk = 1.
EXAFS analysis was conducted in Artemis with the normalized spectra
exported from Athena. The amplitude reduction factor (S02) of 0.82 for Au
and 0.80 for Pd was obtained by fitting the EXAFS data of the respective
metal foils. The simulation of scattering paths was performed with the
ATOMS algorithm with a custom input file created by substituting Au
atoms by Pd according to sample composition and calculating the cell
parameters using Vegard’s law. A correction factor to S02 was introduced
to match sample composition with F-AAS metal concentrations.
Structural parameters were determined by multiple k-weight least-square
fitting and the goodness of fit was determined by observing the reduced
χ2 and R2 statistical parameters.
Experimental Section
Synthesis of supported AuPd nanoparticles.
Gold and palladium monometallic and bimetallic nanoparticles of desired
composition were synthesized by mixing a solution of HAuCl4 (3.31 mL,
4.85x10-3 mol L-1), PdCl2 (2.85 mL, 2.25x10-2 mol L-1) and polyvinyl
alcohol (PVA) (1.2 mL, 1% m/v) and reducing with NaBH4 (4.02 mL, 0.1
mol L-1). After mixing the solutions were allowed to react for 30 min
before adding a 50 mL aqueous suspension of 1.0 g of the amino-
functionalized silica-coated magnetite support (Fe3O4@SiO2-NH2)24 and
stirring at 25 °C for 2 h. The solid was magnetically separated and
resuspended on 25 mL of 60 °C deionized water twice and 25 mL
ethanol twice, and magnetically separated after each resuspension and
dried under air.
Catalytic experiments
The oxidation reactions were performed using a modified Fischer-Porter
100 mL glass reactor. In a typical solventless reaction, the glass reactor
was loaded with the supported AuPd-catalyst (0.75 mg Au + Pd) and
benzyl alcohol (9.6 mmol). The reactor, immersed in an oil bath at
373.15K, was loaded with 6 bar O2. The temperature was maintained by
Calcination and calcination-reduction post-synthesis treatment. The
samples (~500 mg) were thermally treated for 2 h under air with a
heating ramp of 20 °C min-1 up to 500 °C. After cooling to 100 °C the
samples were kept in a desiccator. A portion of calcined catalyst samples
was reduced in hydrogen flow. The sample (100 mg) was added to a
quartz tube (20 cm length and 5mm width) filled with quartz wool. The
tube was introduced in a CATLAB-PCS system (Hiden Analytical) and
hydrogen with a total flow of 50 mL min-1 was introduced. A heating ramp
of 20 °C min-1 up to 500 °C was applied and the sample was left at
500 °C for 30 min.
placing the oil bath on
a hot-stirring plate connected to a digital
temperature controller (ETS-D5 IKA). The reactions were conducted
under magnetic stirring, using Teflon-coated magnetic stir bar. At set
times, the catalyst was magnetically recovered by approaching a magnet
to the reactor wall, the oxygen pressure was relieved and aliquots of the
reaction mixture were recovered with a syringe. The reaction products
were analyzed by gas chromatography (GC) and compared to standards
for the determination of conversion and selectivity using p-xylene as
standard.
Characterization
The total metal concentration in the catalysts was determined by FAAS
on a Shimadzu AA-6300 atomic absorption spectrometer. TEM and
STEM analysis were conducted using a JEOL JEM 2100F microscope
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Acknowledgements
The authors are grateful to the Brazilian agencies FAPESP and
CNPq for financial support and indebted to the Brazilian
Nanotechnology National Laboratory (LNNano, Campinas,
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Keywords: gold • palladium • bimetallic • oxidation • catalysis
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10.1002/cctc.201900553
ChemCatChem
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Dealloying and segregation of PdO
by thermal treatment in air, confirmed
by XRD, EXAFS and XPS, was found
to be a better catalysts than AuPd
(1:4) alloyed NPs for the oxidation of
benzyl alcohol, which suggest a
contribution of PdO phase that was
not correlated before to an increase of
activity in AuPd catalysts
Tiago A. G. Silva, Camila P. Ferraz,
Renato V. Gonçalves, Erico Teixeira-
Neto, Robert Wojcieszak, Liane M.
Rossi*
Page No. – Page No.
Restructuring of gold-palladium
alloyed nanoparticles: a step towards
more active catalysts for oxidation of
alcohols
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